1. Field of the Invention
The present invention relates to optical semiconductor elements such as a light emitting element, a laser element, and a color display element, as well as to a fabricating method therefor.
2. Description of the Related Art
In manufacture of light emitting elements in the blue and ultra-violet ranges, only III-nitride compound semiconductor and II-selenide/sulphide compound semiconductor have been used or are expected to be used.
Light emitting elements manufactured through use of these compound semiconductors materials have the following features.
(1) (Al--Ga--In)N alloy crystals classified as III-nitride compound semiconductors:
(a) These materials emit light in spite of their considerably high defect density. The wavelength of the emitted light is in the range of 390 to 430 nm. PA1 (b) A 450 nm blue-light emitting diode is already in practical use. PA1 (c) Continuous laser oscillation of a 408 nm blue-light laser diode at room temperature has been reported. PA1 (a) These materials have excellent lattice matching with a GaAs substrate, and can be grown at low temperature. PA1 (b) These materials emit light having a wavelength of 430 to 500 nm. PA1 (a) Manufacture of these materials requires a high temperature (.about.1200.degree. C.). PA1 (b) Since the cleavage characteristic differs from that of a sapphire substrate, formation of an end surface of a resonator is difficult. PA1 (c) There exists no substrate whose lattice matches that of this material. PA1 (d) Since the active layer is formed of In-doped GaN, the wavelength of emitted light is large. PA1 (e) The threshold for laser oscillation is high. PA1 (f) Formation of p-type thin film having a low resistance is difficult. PA1 (g) Since the high resistance of the p-type layer causes concentration of supplied voltage to an interface between the p-type layer and an electrode, the operating voltage is considerably high. PA1 (a) The lifetime of a laser diode made of these materials is very short. PA1 (b) Practical use of these materials is considered difficult, in view of very slow progress during an extremely long research period (study started in 1980).
(2) (Zn--Cd--Mg)(Se--S) alloy crystals classified as II-selenide/sulphide compound semiconductors:
However, the III-nltride and II-selenide/sulphide compound semiconductors have a drawback in that mixture of oxygen causes a serious problem.
Further, the III-nitride and II-selenide/sulphide compound semiconductors have the following individual problems.
(1) (Al--Ga--In)N alloy crystals classified as III-nitride compound semiconductors:
(2) (Zn--Cd--Mg)(Se--S) alloy crystals classified as II-selenide/sulphide compound semiconductors: